When data or files may be updated or used for testing, etc., point in time copying is used to preserve an original copy of the data as of one point in time. Point in time copying is conducted in a data storage system to preserve the data without waiting for all the data to be physically copied. At a point in time, the data at that time is considered original data, and any subsequent updates to the data modify that data, which is then called updated data. Access to the point in time data may be conducted with the original point in time copy directly from the source if the data has not been updated, and from the target if the original data at the source was updated.
Point in time copying is as of a point in time, unlike synchronous mirroring which is a continuous process of copying data as it updated, but which prevents any updating from occurring by failing to complete the updating storage transaction for the data at a source until after that updating data has also been stored at a target. Asynchronous mirroring also is continuous, but may appear to be quicker, and is a complex process that requires that the updating data is first stored by the source data storage, and requires that safeguards are in place to assure that it will ultimately be stored at the target data storage.
Customers would prefer the point in time copy target to be at a location remote from the source, or at a separate data storage machine. Copying point in time data to a remote location or to another data storage machine typically is accomplished by a host system which copies the data to the remote location or another data storage machine, and the data is typically not immediately available from the target, which must wait until all the point in time data has been copied.